I. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method of uplink scheduling for data communication.
II. Description of the Related Art
Wireless communications systems employ a number of geographically distributed, cellular communication sites or base stations. Each base station supports the transmission and reception of communication signals to and from stationary or fixed, wireless communication devices or units. Each base station handles communications over a particular region commonly referred to as a cell/sector. The overall coverage area for a wireless communications system is defined by the union of cells for the deployed base stations. Here, the coverage areas for adjacent or nearby cell sites may overlap one another to ensure, where possible, contiguous communications coverage within the outer boundaries of the system.
When active, a wireless unit receives signals from at least one base station over a forward link or downlink and transmits signals to at least one base station over a reverse link or uplink. There are many different schemes for defining links or channels for a cellular communication system, including, for example, TDMA (time-division multiple access), FDMA (frequency-division multiple access), and CDMA (code-division multiple access) schemes. In CDMA communications, different wireless channels are distinguished by different channelization codes or sequences that are used to encode different information streams, which may then be modulated at one or more different carrier frequencies for simultaneous transmission. A receiver may recover a particular stream from a received signal using the appropriate code or sequence to decode the received signal.
For voice applications, conventional cellular communication systems employ dedicated links between a wireless unit and a base station. Voice communications are delay-intolerant by nature. Consequently, wireless units in wireless cellular communication systems transmit and receive signals over one or more dedicated links. Here, each active wireless unit generally requires the assignment of a dedicated link on the downlink, as well as a dedicated link on the uplink.
With the explosion of the Internet and the increasing demand for data, resource management has become a growing issue in cellular communication systems. Next generation wireless communication systems are expected to provide high rate packet data services in support of Internet access and multimedia communication. Unlike voice, however, data communications are relatively delay tolerant and typically bursty. Data communications, as such, do not require dedicated links on the downlink or the uplink, but rather enable one or more channels to be shared by a number of wireless units. By this arrangement, each of the wireless units on the uplink competes for available resources. Resources to be managed in the uplink include the received power at the base station, and the interference created by each user to other users in the same sector or cell, as well as in other sectors or cells, for example. This is in contrast to the resources to be managed on the downlink, including fixed transmit power budgets.
In view of the need for resource management in data communication, it should be noted that the ultimate bit rate in which a communication system operates might be derived using Shannon's limit to information theory. Shannon's limit is based on a number of different parameters. These Shannon's limit parameters include, for example, the total power radiated at the transmitter, the number of antennas at the transmitter and receiver, available bandwidth, noise power at the receiver, and the characteristics of the propagation environment.
The transmission rate of data in a wireless communication system depends on the total power available at the particular wireless unit, the quality of the radio link, and the received power and interference levels that may be tolerated by all the base stations receiving the signal from the wireless unit. Quality of service provisioning will attempt to guarantee a desired throughput or delay for a specific application for each wireless unit. On the other hand, effective resource management enhances the efficiency of the wireless communications system, thereby improving the overall system throughput. Additionally, there may be other tangible benefits to “smart” or “intelligent” channel utilization methods, such as hybrid ARQ and/or incremental redundancy, for example.
Presently, resource management schemes for data applications have concentrated on the downlink. These known solutions have proposed centralizing the operations at the base station or equivalent (e.g., inter-working function). The base station provides a route for all requests from wireless units on the uplink, as well as all responses to the wireless unit on the downlink. Consequently, the base station serves as a focal point for all requests even if the data has to be fetched from another source location. The base station, therefore, may be used as a server for performing a centralized scheduling operation in determining which wireless units receive data, when they may receive the data, for how long they may receive the data, and at what rate they may receive data.
Resource management and channel allocation on the uplink, to date, has been primarily treated as a “distributed control” concern. Here, the base station does not control the operations by assigning service order priorities. The base station, however, may supervise access to the uplink and monitor operations via slow or fast power control. For example, in CDMA2000 1×systems, each wireless unit makes a request for an uplink channel at a specific rate. The base station monitors the interference patterns and determines whether to allow the wireless unit making the request access to an uplink channel. If the wireless unit is granted access, subsequent transmissions may be power controlled. In 1×EV-DO systems, uplink access may be controlled by allowing each wireless unit begins to transmit autonomously, initially at the lowest rate in the rate set. At every subsequent transmission, each wireless unit autonomously doubles its data rate, while the base station continuously manages the channel via power control. If the aggregate received power at the base station or the interference to each wireless unit exceeds a predefined threshold, the base station orders all wireless units to reduce their data rates.
These known schemes for managing resources and channel allocation in data applications on the uplink have a number of shortcomings. Firstly, wireless units on the uplink are not scheduled for gaining access to the base station's resources. The wireless communication system's operation, consequently, is neither efficient nor is its throughput optimized. Moreover, quality of service requirements is considerably more difficult to realize without a scheduling system.
Therefore, a need exists for a scheduling system to manage the base station's resources and channel allocation in data applications with respect to wireless units on the uplink.